1. Field of the Invention
The present invention relates to an optical imaging element, including an optical element that uses a specular reflection by a micromirror, for forming a real image of an object in air on an opposite side of the element; and a display device including such an optical imaging element.
2. Description of the Related Art
Known conventional optical elements for forming an image of a three dimensional or two dimensional actual object, displayed image, or the like as a real image at a position transferred spatially include aspects that use, for example, convex lenses or concave mirrors. However, in order to respond to demands to ensure an appropriate viewing angle, optical elements must have large width dimensions; and on the other hand, it is difficult to use an optical element having a short focal distance due to aberrations and other problems, resulting in a larger depth dimension of the optical system. These considerations unfortunately greatly increase the size of a device that uses the optical element and also result in a larger display device itself. Moreover, it is difficult to completely eliminate aberrations even in the case where the device is enlarged; the spatial position of the real image unfortunately changes when the viewpoint is changed; and the image of the three dimensional actual object distorts.
Recently, to resolve such problems, display devices for floating images using microlens arrays have been developed (for example, see Japanese Published Unexamined Patent Application No. 2005-234240). This technology uses an erect image forming system with unit magnification for a two dimensional image, wherein an optical device, having a size similar to a display surface that displays the two dimensional image, enables a parallel translation of a two dimensional image without distortion. Such technology enables an optical device that is smaller and thinner than a normal lens, which contributes to the compactness of the display device as well. However, a real image of a three dimensional actual object cannot be obtained with this technology.
Therefore, optical elements have been proposed in which each individual optical system included in the erect optical imaging element with unit magnification used by the system recited above is an afocal optical system having an infinite focal distance (for example, see Japanese Published Unexamined Patent Application No. 2005-010755). Such an optical element enables the formation, as a real image, of a specular image of an object, and uses the refracting ability of light by a lens as its basic principle; and therefore this optical element is referred to hereinafter as “refractive real specular image forming element.” Forming a real specular image means that the real image of the three dimensional actual object can be formed without distortion. The refractive real specular image forming element is an optical component including an afocal optical system, having a first lens component and a second lens component arranged on the same optical axis and separated by their respective focal distances, wherein the entrance lens surface and the exit lens surface of the afocal optical system are arranged in an array on the same plane. Combinations have been proposed for the first lens component and the second lens component, including configurations having two convex lenses, one or more optical fiber lenses, etc.